Japanese: the world most difficult-to-read language 日本語、世界一読みにくい言語であろう
I have long been fascinated with how writing systems in the world are related. I am so glad I have found the book called "Ideogram: Chinese Characters and the Myth of Disembodied Meaning" by J. Marshall Unger which has one section dedicated to the comprison between cryptograms and pictograms. Interesting enough, what I can first and foremost conclude from this section is that the most difficult language to read is, in fact, Japanese.
Writing systems like Finnish and Spanish are considered nearly ideal phonographies. English and French, which have numerous "irregular spellings," are less perfectly phonographic. Arabic and Hebrew, which usually omit vowel signs, have fewer such regularities but require you to fill in a lot of phonographical information on the basis of your knowledge of the structure of the language; hence, they are even less phonographic. But all systems that use Chinese characters are ipso facto logographic to an extent that alphabetic or syllabic writing systems can never approach. In fact, Japanese is the most logographic writing system of all, because Chinese characters take different readings in Japanese writing depending on the context. Japanese happens to be more logographic than Chinese although some might feel that it should be reversed because Japanese writing also use kana, which are highly phonographic. This is, however, subject to subjective judgement.
According to the paragrapgh above, we can safely say that Japanese is the most difficult language in the world in term of reading.